1. Field of the Invention
The present invention relates to thin film magnetic memory devices, and more particularly to a thin film magnetic memory device provided with a memory cell having a magnetic tunnel junction and a program element for storing information in a fixed manner.
2. Description of the Background Art
A magnetic random access memory device (MRAM device) has attracted attention as a memory device capable of non-volatile data storage with low power consumption. The MRAM device stores data in a non-volatile manner using a plurality of thin film magnetic elements formed on a semiconductor integrated circuit, and permits random access to the respective thin film magnetic element.
In particular, it has been reported that provision of memory cells (hereinafter, also referred to as “MTJ memory cells”) formed of thin film magnetic elements utilizing magnetic tunnel junctions (MTJ) significantly improves the performance of the MRAM device. The MTJ memory cell stores data as it is magnetized, by a magnetic field generated by a data write current, in a direction corresponding to data to be written. Such an MRAM device is disclosed, e.g., in “A 10 ns Read and Write Non-Volatile Memory Array Using a Magnetic Tunnel Junction and FET Switch in each Cell”, 2000 IEEE ISSCC Digest of Technical Papers, TA7.2.
A memory device is generally provided with a program element, such as a fuse element, for the purposes of fixedly storing information necessary for redundancy repair, tuning information of an internal voltage and others. In the MRAM device capable of storing data in each memory cell in a non-volatile manner, it is possible to use an excessive MTJ memory cell to constitute such a program element.
Alternatively, Japanese Patent Laying-Open No. 2002-117684 discloses, focusing on an insulating film forming a magnetic tunnel junction, a configuration for programming information in a fixed manner by causing breakdown of the insulating film.
In the case of forming the program element with an excessive MTJ memory cell, however, data stored in the MTJ memory cell may be lost during heat treatment after completion of a wafer process, through burn-in and packaging steps, before shipment.
As a program element permitting more stable storage of information, a fuse element which can be blown with laser irradiation in a wafer state is known. The MRAM device, compared to a normal memory device, requires additional depositing and processing steps dedicated to formation of the MTJ memory cells. Thus, the number of other steps should be made as small as possible. As such, it is desirable that formation of such a fuse element does not require dedicated manufacturing steps.
Furthermore, the memory device is tested in each of wafer state, packaged state, and others. As such, there is a demand for a program element which can program information accumulatively based on results of the plurality of tests.